To understand the relationship between feeding schedule and small intestinal function; understand the regulation of gastrointestinal function and the nature of biorhythms. This objective will be approached from 3 directions. 1) To describe more completely how the levels of activity of brush border enzymes and transport systems change during the rhythm period. 2) To determine which component(s) of the feeding schedule are the external cue(s) for these rhythms. 3) To determine which component(s) of the alimentary tract and endocrine system are involved in the international mediation of the feeding cue.